The present invention relates to a fluorescent lamp device which is used for backlighting of liquid crystal displays, for example.
In the case of employing a fluorescent lamp as a light source for backlighting of a liquid crystal display, the envelope temperature of the lamp may sometimes exceed an optimum operating temperature owing to an ambient temperature rise and a temperature rise in the display which is caused by heat generation of the lamp itself. FIG. 1 shows how the mercury resonance radiation intensity of the fluorescent lamp varies with temperature variations therein, and in this instance, the optimum operating temperature is about 40.degree. C. As the envelope temperature of the fluorescent lamp becomes higher than the optimum operating temperature, the mercury resonance radiation intensity of the lamp decreases and its brightness lowers accordingly.
To avoid this, it is a general practice in the prior art to provide radiator plates or radiation fins around the fluorescent lamp or to air-cool the lamp by means of a radiation fan so that the envelope temperature of the lamp remains below its optimum operating temperature. Another method that has been proposed is to provide a Peltier element for cooling the fluorescent lamp during its lighting.
However, since the optimum operating temperature of the fluorescent lamp rises as the operating temperature range of the liquid crystal display increases, it is difficult to maintain the envelope temperature of the lamp at the optimum operating temperature at all times through use of the above-mentioned conventional method in which radiator plates or radiation fins are provided around the fluorescent lamp or the lamp is air-cooled by a radiation fan, and the envelope temperature of the lamp may go over its optimum operating temperature, causing decrease in its brightness. With the method which employs a Peltier element for cooling the lamp during its lighting, there are times when the envelope temperature of the fluorescent lamp is held lower than its optimum operating temperature by excessive cooling, resulting in a decrease rather than an increase in the brightness.